An adjustable dockboard, as shown in U.S. Pat. No. 3,117,332, includes a ramp having its rear end hinged to a dock. The ramp is biased upwardly to an inclined position by a spring assembly, and a manually releasable holddown device holds the ramp against elevation. Hinged to the front edge of the ramp is an extension lip which is adapted to swing from a pendant position, in which the lip hangs downwardly from the front edge of the ramp, to an elevated position in which the lip forms an extension to the ramp. The lip, when in the extended position, is adapted to engage the bed of a truck or carrier and bridge the gap between the ramp and the truck to enable material handling equipment to move between the dock and the truck.
In the dockboard, as disclosed in U.S. Pat. No. 3,117,332, the extension lip is automatically raised to its elevated position by a lip lifting and latching mechanism which is actuated by the upward movement of the ramp when the holddown device is released. With the lip extended and the ramp in the upwardly inclined position, the ramp is walked down by the operator until the lip engages the bed of the truck. The engagement of the lip with the bed of the truck releases the weight from the lip latching mechanism, thereby releasing the latching mechanism, so that when the truck pulls away from the dock the lip will automatically return to its pendant position.
As disclosed in U.S. Pat. No. 3,117,332, the lip lifting mechanism can take the form of a flexible cable attached between the supporting frame and a crank arm pivoted to the ramp and engageable with the underside of the lip. When the ramp is elevated through use of the counterbalancing spring assembly, the cable becomes taut to pivot the crank arm and thereby pivot the lip toward the extended position.
As the lip has substantial weight, a lip assist or lip counterbalancing mechanism, such as that disclosed in U.S. Pat. No. 3,203,002, can be incorporated to aid in swinging the lip toward its extended position.